The technology of forming a metallic conductive layer on a ceramic surface has been employed widely in the manufacture of electronic parts and other articles. One of such methods is the method known as electroless plating. As ceramics are not receptive to electroless plating baths, it is necessary that the surface of a ceramic substrate be previously treated with a catalyst metal such as palladium, silver or the like prior to the formation of a metallic layer by electroless plating. The methods heretofore known for applying a catalyst metal to the substrate surface include (a) the process which comprises dipping a ceramic substrate in a solution of the catalyst metal in acidic aqueous medium, (b) a process in which the ceramic substrate is treated with a bath prepared by dissolving or dispersing a catalyst metal compound in an organic medium by a suitable technique such as dipping, brushing or spraying and the substrate so treated is then heated, and (c) a process in which a composition prepared by dissolving or dispersing the catalyst metal compound in an organic or other vehicle is printed on the substrate and the printed substrate is then heated. However, these known methods for catalyst metal pretreatment have at least one of the following disadvantages that must be overcome.
(a) The process is costly because the expensive catalyst metal compound must be provided in high concentration.
(b) The composition containing the catalyst metal compound has a poor storage stability.
(c) The deposition and adhesive characteristics of the electroless plating metal applied after application of the catalyst metal with respect to the ceramic substrate are not fully satisfactory.
(d) There is a serious limitation to the type of ceramic materials that can be treated.
(e) When the catalyst metal is applied to the ceramic substrate by screen printing, partial dipping or the like, the dimensional accuracy of the metal plating layer is sacrificed.